Method for producing polyesters from benzenedicarboxylic acid and alkylene oxide

ABSTRACT

A polyester having a high quality is produced by reacting a benzendicarboxylic acid with an alkylene oxide in an aqueous medium containing an alkali metal ion of 2.7 to 10 mole per 1 l of water, extracting the reaction mixture with an organic solvent to separate diglycol ester, concentrating or/and crystallizing the extracted solution and then effecting polycondensation.

States atent lzawa et al.

I |March 13, 1973 METHOD FOR PRODUCING POLYESTERS FROMBENZENEDICARBOXYLIC ACID AND ALKYLENE OXIDE Inventors: Nobuo lzawa;Yasuhiro Iizuka; Yoshiaki Kubota, all of Osaka-fix,

Japan Assignee: Kanegafuchi Boseki Kabushiki Kaisha, Tokyo, Japan Filed:Dec. 1, 1970 Appl. No.: 94,165

Foreign Application Priority Data Dec. 8, 1969 Japan ..44/98775 Dec. 26,1969 Japan ..45/1232 Dec. 26, 1969 Japan ..45/l233 US. Cl. ..260/75 M,260/75 EP, 260/475 P, 260/475 PR Int. Cl. ..C08g 17/7 Field of Search..260/75 M, 475 P, 475 PR, 75 ET [56 References Cited UNITED STATESPATENTS 3,008,981 11/1961 Vaitekunas ..260/475 3,052,711 9/1962 Glogauet al. 260/475 3,120,560 2/1964 Keck ....260/475 3,268,575 8/1966 Keck..260/475 FOREIGN PATENTS OR APPLICATIONS Canada Japan PrimaryExaminer-Melvin Goldstein Att0rney-Woodhams, Blanchard & Flynn [57]ABSTRACT 9 Claims, No Drawings METHOD FOR PRODUCING POLYESTERS FROMBENZENEDICARBOXYLIC ACID AND ALKYLENE OXIDE The present inventionrelates to a method for producing polyesters from a benzenedicarboxylicacid and an alkylene oxide.

As a method for producing a polyester from a benzenedicarboxylic acidand an alkylene oxide, the following processes have been proposed:

1. A benzenedicarboxylic acid and an alkylene oxide are reacted byheating and successively a polycondensation is effected.

2. A benzenedicarboxylic acid and an alkylene oxide are reacted byheating and then diglycol ester is separated by crystallization from asolvent and then polycondensed.

In the above process 1, a catalyst, such as, a tertiary amine, an alkalimetal and the like used in the original stage of the reaction remainsand causes a side-reaction in the polycondensation, so that theresulting polymer is colored, the viscosity is not increasedsatisfactorily and the melting point is low, and consequently a highquality of polyester cannot be obtained.

In the above process 2, impurities are removed from the reaction productand consequently, a high quality of polyester can be readily obtained,but in general, the separation step for purification (for example,crystallization and the like) is troublesome and further the dissolutionloss of diglycol ester is large and such a process is not advantageouscommercially. Accordingly, it is considerably desired to simplify such aseparation step.

British Pat. No. 623,669 and U.S. Pat. No. 3,101,366 have proposed thata benzenedicarboxylic acid and an alkylene oxide are reacted in anaqueous medium in the presence of an alkali metal catalyst in theprocess for producing polyester. In these processes, the reactionproducts contain a large amount of diethylene glycol and diethyleneglycol ester and the production of such substances is verydisadvantageous and if the separation for purifying diglycol estercontaining a large amount of these substances is effected simply, thepolyester obtained by polymerizing such diglycol ester contains etherbond and the melting point is low and the heat stability and weatherresistance are poor. Thus such polyester cannot be used practically.Therefore, unless diglycol ester obtained in such a process is subjectedto troublesome purification steps, commercially useful polyester cannotbe produced.

An amount of an alkali metal catalyst in the reaction of terephthalicacid with ethylene oxide in the presence of an alkali metal catalyst inan aqueous medium in the above described process, is within or near thesaturation solubility of alkali metal salt of terephthalic acid, whichis shown in the following Table 1. This is based on the followingreason. It has been believed that the alkali metalsalt or terephthalicacid present in an amount of higher than the solubility of alkali metalsalt of terephthalic acid has no function for the reaction.

2.7 mol/l In order to solve the above described various demerits, theinventors have made various investigations and found the followingfacts:

5 1. The presence of alkali metal salt of terephthalic acid of more thanthe solubility is effective for the reaction.

2. By an extraction with an organic solvent, diglycol ester and a smallamount of by-produced ethylene glycol can be easily separated from thereaction system.

The object of the present invention is to provide a method for producinga high quality of polyester for shaping into fiber or film.

The other object of the present invention is to provide a method forproducing commercially improved polyester.

The present invention is characterized in that a benzenedicarboxylicacid and an alkylene oxide are reacted in an aqueous medium containingan alkali metal ion of 2.7 to mole per 1 l of water and from thereaction mixture diglycol ester is separated by an extraction with anorganic solvent and then separated 2 by concentration or (and)crystallization and thereafter polycondensed.

A particularly essential requirement for performing the reaction of thepresent invention is the presence of an alkali metal ion of 2.7 to 10mole, preferably, 3 to 8 mole per 1 l of water. If the concentration ofalkali metal ion is less than 2.7 mol/l-H O, a side-reaction ofproducing diethylene glycol increases and a high quality polyestercannot be obtained. On the other hand, if the concentration of alkalimetal ion is more than 10 mol/l-H O, the production of an insoluble saltof dicarboxylic acid increases and the stirring becomes difficult andtherefore, the side-reaction increases.

Alkali metal ions means lithium, sodium, potassium, rubidium and cesium,and they are used alone or in admixture and particularly, lithium andsodium are preferable, because they are high in the reaction rate andlittle in the side-reaction. Among them, lithium alone or in admixtureis particularly preferable. In the practical reaction, the abovedescribed alkali metals are added to the reaction system in a givenamount as an alkali metal salt, such as, hydroxides, carbonates, boratesand the like. Of course, the salt may be added in the form of an alkalisalt of benzenedicarboxylic acid.

If a conventional catalyst of a tertiary amine is used in the abovedescribed range of concentration, the reaction system is considerablycolored, while the alkali metal catalyst does not cause such acoloration.

The benzenedicarboxylic acids to be used in the present invention arearomatic dicarboxylic acids, such as, terephthalic acid, isophthalicacid and the like and they are used alone or in admixture, but the otherdicarboxylic acids, such as aliphatic dicarboxylic acid or aliphatic andaromatic oxycarboxylic acids may be used together with the abovedescribed aromatic dicarboxylic acid in an amount of less than molpercent based on the aromatic dicarboxylic acid. The amount of thesedicarboxylic acids is more than equivalent of the alkali metal ion butif the amount is more than five times by weight of the reaction aqueoussolution, the stirring is difficult and such an amount is not preferablein view of the operation.

The alkylene oxide may be fed in a vapor form or under a sufficientpressure to maintain the alkylene oxide in a liquid phase. Furthermore,the alkylene oxide may be charged the total amount to be used in thereaction or added gradually.

As alkylene oxides, use may be made of ones having two to six carbonatoms in molecule and particularly, ethylene oxide and propylene oxideare used. In addition to these oxides, butylene oxide, amylene oxide,hexene oxide and thelike can be used.

If the reaction temperature is too low, the reaction rate is slow, whileif the reaction temperature is too high, the reaction occurs rapidly andthe regulation of temperature is difficult and the side-reaction occurs,so that even if the polymerization is effected, a high quality ofpolyester cannot be obtained. Therefore, 60 140 C is preferable and 70130 C is most preferable.

Air in the reaction vessel is previously substituted with an inert gasof nitrogen for safety sake but in the reaction the gaseous phase in thereaction vessel may be occupied by water vapor and alkylene oxide.

After the reaction, after or before water is distilled off from thereaction mixture, an organic solvent alone or in admixture, which candissolve diglycol ester but cannot dissolve alkali metal salt ofcarboxylic acid, is added to the reaction mixture and the undissolvedsubstances are separated by a centrifugal separator, filter and thelike. When a solvent is added before water is distilled off, it ispreferable to add a solvent which can form an azeotropic mixture withwater and in this case water can be easily and completely removed. It isdesirable to remove water completely as far as possible and in the caseof incompletion, an alkali metal salt of carboxylic acid is dissolvedtherein and is liable to remain in diglycol ester and when such diglycolester is polycondensed by heating, a coloration occurs and only anopaque polyester having a low viscosity is formed. As the organicsolvent to be used in the present invention, organic solvents having aboiling point of 50 170 Care preferable in view of operation. Esters,such as, methyl acetate, ethyl acetate, propyl acetate, butyl acetate,ethyl formate and the like; ethers, such as tetrahydrofuran, dioxane,dipropyl ether, dibuty] ether and the like; ketones, such as, acetone,methyl ethyl ketone, methyl butyl ketone, cyclohexanone and the like;alkyl benzenes, such as, benzene, toluene, xylene, and the like;halogenated hydrocarbons, such as, chloroform, carbon tetrachloride,dichloroethane, trichlene, chlorobenzene and the like; nitriles, suchas, acetonitrile, propionitrile; alcohols, such as, methanol, ethanol,propanol, butanol, amylalcohol, hexanol, cyclohexanol, and the like maybe used alone or in admixture. Among them, esters, ketones andhalogenate hydrocarbons are preferable and they are sufficient in asmaller amount than the other solvents and can extract more completely.The solvents other than these solvents are low in the solubility ofdiglycol ester, so that they must be used in a large amount, or havelower ability in the separation of diglycol esters from the reactionmixture, so that the alkali metal salt of carboxylic acid isincorporated in the resulting diglycol ester, or the amount of unreactedbenzenedicarboxylic acid and monoglycol ester thereof containedincreases and the stability of diglycol ester is low and the qualitydecreases during the storage. Particularly, the heat stability is lowerin the melted stage and when it is necessary to store or ship diglycolester in the melted state, a coloration occurs, the oligomer increasesand compound having ether bonds increases, so that the quality isdegraded.

The amount of solvent to be used is admissible in an amount enough todissolve diglycol ester present in the reaction mixture, but variesdepending upon the solvent, treating temperature and process and ingeneral, the solvent is used in an amount of one to 50 times of thereaction mixture, preferably, two to 30 times and in the above describedpreferable solvents, two to 20 times is generally used. The higher thetreating temperature, the larger the solubility of diglycol ester is andit is preferably to effect the treatment at a temperature near theboiling point of the solvent. The extraction treatment may be carriedout in a batch system or a continuous system and the flows of thesolvent and the substance to be extracted may be parallel, counter orcross.

The undissolved substances separated involve unreacted dicarboxylicacid, alkali metal salt of dicarboxylic acid and the like and they canbe supplied again to the reaction.

After the undissolved substances are separated, the extracted solutionis concentrated by distilling off the solvent to obtain a mixture ofdiglycol ester and a small amount of by-produced ethylene glycol.Alternatively, the resulting extract or the solution concentrated tosome extent is cooled to separate diglycol ester by crystallization.

The resulting diglycol ester or the mixture of diglycol ester and asmall amount of ethylene glycol, directly or if necessary, after beingpurified with water or an organic solvent or a mixture thereof, ispolycondensed at a temperature of higher than 200 C by adding apolymerization catalyst to form a high quality of polyester. When adiglycol ester or a mixture of diglycol ester and ethylene glycol isformed by effecting a concentration operation, it is advantageous forimmediately effecting the polycondensation or shipping or storage toobtain said diglycol ester or the mixture in a liquid form, but it isadmissible to obtain same in a solid or paste form. Furthermore, thepolymerization catalyst may be added before the concentration of theextracted solution.

According to the method of the present invention polyesters havingexcellent heat stability and weather resistance and no coloration can beproduced commercially. If the requirements of the reaction for producingdiglycol ester in the present invention are not satisfied, only coloreddiglycol ester having a large number of unstable ether bonds isobtained, so that the simple and efficient process in the presentinvention, wherein diglycol ester is separated by an extraction with anorganic solvent and then concentrated or (and) separated bycrystallization, thereafter polycondensed cannot be used. It dependsupon the quality of the starting material of dicarboxylic acid, whethercrystallization and other purification steps should be carried out ornot after the extraction. In the above described process for producingdiglycol ester according to the present invention, the by-production ofcolored substance and other substances which need the separation ofcrystallization are very few. Accordingly, when a relatively highquality of starting material is used, it is preferable to adopt theconcentration operation which is more efficient and inexpensive than thecrystallization operation.

Moreover, when the process of the present invention in which diglycolester is extracted with an organic solvent and then concentrated or(and) crystallized and thereafter polycondensed, is not adopted, it isnecessary in order to separate a large amount of reaction catalyst fromthe resulting product, to repeat the crystallization of diglycol estermany times by dilution of the reaction product with a large amount ofwater and to concentrate the aqueous solution (mother liquid) which ishigh in heat capacity and in an evaporation cost. Furthermore, whenthere are impurities (colored substance in the starting material ofdicarboxylic acid, carbonyl compound and the like) which are difficultin the separation by recrystallization from aqueous medium, it isnecessary to add a purification step of recrystallization by means of anorganic solvent separately, so that such a means is troublesome and isnot advantageous commercially. Accordingly, such a process cannot attainthe merits of the present invention in which by-products in theproduction of diglycol ester are very few and colored substances are notformed and a high efficiency can be attained.

The following examples are given in illustration of this invention andare not intended as limitations thereof.

It is apparent that many variations may be made in the process of thisinvention without departing from the spirit and scope thereof. The partin examples means by weight and the intrinsic viscosity is measured inorthochlorophenol at 30 C and the melting point of the polymer ismeasured on a heat plate by a polarization microscope.

EXAMPLE 1 24 parts of sodium hydroxide was dissolved in 100 parts ofwater to prepare 6 mol/] of an aqueous solution of sodium hydroxide. Theresulting solution and 130 parts of highly pure terephthalic acidcontaining about 25 ppm of 4-carboxybenzaldehyde and 5 ppm of ash werecharged in an autoclave equipped with a stirrer and air in the autoclavewas substituted with nitrogen and then the mixture was heated at 100 Cunder atmospheric pressure. Ethylene oxide was introduced under apressure of 4 kg/cm into the autoclave for 40 minutes while stirring.The autoclave was returned to atmospheric pressure and unreactedethylene oxide was recovered and further the heating was continued toremove water. Then 500 parts of n-butyl acetate was added to thereaction mixture and the resulting mixture was heated at 120 C and thenfiltered off the undissolved substances, which were 90 parts. Theundissolved substances involved terephthalic acid, sodium terephthalateand sodium salt of monoester, which were supplied again to the nextreaction. The filtrate was heated to evaporate and recover n-butylacetate. The residue was added with 0.04 part of antimony acetate andthe mixture was maintained. at 280 C under 0.5 mmI-lg for 3 hours toobtain transparent polyethylene terephthalate having an intrinsicviscosity of0.67 and a melting point of 265 C.

Before the extraction with n-butyl acetate, a sample of the reactionmixture was determined with respect to ethylene glycol bygaschromatography. Said sample was hydrolyzed and then determined withrespect to diethylene glycol by gaschromatography. As the result, 47parts of ethylene oxide was reacted and the conversion into ethyleneglycol was 12 percent and the conversion into diethylene glycol anddiethylene glycol ester was only 2.2 percent.

COMPARATIVE EXAMPLE 1 After the reaction was effected under the samecondition as described in Example 1, the autoclave was returned toatmospheric pressure and the unreacted ethylene oxide was recovered andthen a part of the reaction mixture was taken out and polymerized undera pressure of 0.5 mmI-Ig at 280 C for 3 hours by using antimony acetateas a catalyst. The resulting polymer was yellowish brown and opaque andhad an intrisnic viscosity of 0.36.

On the other hand, when the reaction mixture'was heated and filtered,the filtrate was cooled and solidified and then subjected to acentrifugal separator to obtain crystals, which were recrystallizedtwice from water and subjected to a centrifugal separator. The resultingcrystals were washed with water at 5 C twice and dried. The transparentcrystals were polymerized under a pressure of 0.5 mmHg, at 280 C for 3hours by using a catalyst of antimony acetate to obtain colorlesstransparent polyethylene terephthalate having an intrisnic viscosity of0.67 and a melting point of 265 C.

COMPARATIVE EXAMPLE 2 8 parts of sodium hydroxide was dissolved in partsof water to prepare 2 mol/l of an aqueous solution and 80 parts ofhighly pure terephthalic acid was added thereto and ethylene oxide wassupplied in the same manner as described in Example 1 for 60 minutes.The autoclave was returned to atmospheric pressure and unreactedethylene oxide was recovered and the residue was heated to evaporatewater. Then 400 parts of n-butyl acetate was added thereto andundissolved substances were filtered off at C. The filtrate was heatedto distill off and recover n-butyl acetate and then 0.03 part ofantimony acetate was added to the residue and the resulting mixture washeated at 280 C. under a pressure of 0.5 mmI-Ig for 3.5 hours to obtainpolyethylene terephthalate having an intrisnic viscosity of 0.58 and amelting point of 259 C, which was colored light yellow, because thispolymer contained a large amount of unstable ether linkage.

COMPARATIVE EXAMPLE 3 24 parts of sodium hydroxide was dissolved in 100parts of water in the same manneras described in Example and theresulting solution and parts of terephthalic acid were charged in theautoclave. Air in the autoclave was purged with nitrogen and the mixturein the autoclave was heated at C. Then ethylene oxide was supplied undera pressure of 7 Kg/cm for 15 minutes while stirring. The autoclave wasreturned to atmospheric pressure and the reaction mixture was taken outand analyzed. 54 parts of ethylene oxide was reacted and the conversioninto ethylene glycol was 37 percent and the conversion into diethyleneglycol was 17 percent.

EXAMPLE 2 12 parts of lithium hydroxide was dissolved in 100 parts ofwater to prepare 5 mol/l of an aqueous solution. The resulting solutionand 90 parts of highly pure terephthalic acid were charged into anautoclave equipped with a stirrer. Air in the autoclave was purged withnitrogen and the mixture was heated at 100 C under atmospheric pressure.Then ethylene oxide was supplied thereto under a pressure of 2.5 Kg/cmfor minutes. The autoclave was returned to atmospheric pressure andunreacted ethylene oxide was recovered. Thereafter, l,000 parts ofn-butyl acetate was added thereto and water was removed as an azeotropicmixture (B.P. 90.2 C, water 28.7 percent) with n-butyl acetate and thenthe undissolved substances were filtered off, which were 79 parts. Theundissolved sub stances were used in the next reaction. The filtrate wasconcentrated to recover n-butyl acetate. 0.02 part of antimony acetatewas added thereto and the resulting mixture was heated at 280 C under apressure of 0.5 mml-lg for 3 hours to obtain colorless transparentpolyethylene terephthalate having an intrisnic viscosity of0.69 and amelting point of 265 C.

A sample of the reaction mixture before the extraction with n-butylacetate was analyzed. 22 parts of ethylene oxide was reacted and theconversion into ethylene glycol was 9 percent and the conversion intodiethylene glycol and diethylene glycol ester was 1.7 percent.

EXAMPLE 3 33.6 parts of potassium hydroxide was dissolved in 100 partsof water to prepare 6 mol/l of an aqueous solution. The solution and 100parts of highly pure terephthalic acid were charged in an autoclaveequipped with a stirrer and air in the autoclave was purged withnitrogen. The mixture was heated at 100 C under atmospheric pressure.Ethylene oxide was supplied under a pressure of 4 Kg/cm for 30 minutes.The autoclave was returned to atmospheric pressure and unreactedethylene oxide was recovered and the residue was continuously heated toremove water. Then 800 parts of methyl ethyl ketone was added theretoand the mixture was heated at 75 C and undissolved substances werefiltered off and the filtrate was concentrated to recover methyl ethylketone. 0.01 part of antimony oxide was added and the mixture wasmaintained at 280 C under a pressure of 0.5 mmHg for 3.5 hours to obtaincolorless transparent polyethylene terephthalate having an intrisnicviscosity of 0.64 and a melting point of 264 C.

A sample of the reaction mixture was analyzed before the extraction withmethyl ethyl ketone and 26 parts of ethylene oxide was reacted and theconversion into ethylene glycol was 18 percent and the conversion intodiethylene glycol ester was 2.9 percent.

EXAMPLE 4 12 parts of lithium hydroxide was dissolved in 100 parts ofwater to prepare the 5 mol/l solution and the resulting solution and 150parts of highly pure terephthalic acid were charged in an autoclaveequipped with a stirrer and air in the autoclave was purged withnitrogen and the pressure was reduced and the mixture was graduallyheated to C. Then ethylene oxide was supplied under a pressure of 4Kg/cm while stirring for 110 minutes. The autoclave was returned toatmospheric pressure and unreacted ethylene oxide was recovered and theheating was continued to distill off the greater part of water. 850parts of dichloroethane was added thereto and the mixture was heated tothe boiling point to distill off water completely and undissolvedsubstances were filtered off. The filtrate was concentrated to recoverdichloroethane. To the resulting concentrate were added 50 parts ofhighly pure terephthalic acid and 0.03 part of antimony acetate and themixture was heated gradually and the produced was evaporated whilemaintaining 3 Kg/cm gauge. After reaching 275 C, the polymerization waseffected under a reduced pressure of 0.3 mml-lg for 3.5 hours to obtaincolorless transparent polyethylene terephthalate having an intrinsicviscosity of 0.65 and a melting point of 267 C. Before the extractionwith dichloroethane, a sample of the reaction mixture was analyzed. 60parts of ethylene oxide was reacted and the conversion into ethyleneglycol was 6 percent and the conversion into diethylene glycol anddiethylene glycol ester was only 0.9 percent. This is the reason why themelting point of the resulting polymer is high.

On the other hand, when terephthalic acid and ethylene oxide werereacted in the same condition as described above except that thereaction temperature was 40 C and the pressure was 2.5 Kg/cm thefluidity of the reaction mixture of a slurry state was poor and thestirring was very difficult and therefore the reaction was very slow andwas not practical.

EXAMPLE 5 In parts of water was dissolved 7.2 parts of sodium hydroxideto prepare 3 mol/l of an aqueous solution. The resulting solution wasintroduced into an autoclave equipped with a stirrer together with 40parts of light yellow crystals of crude terephthalic acid prepared fromp-xylylene by air oxydation containing about 5,000 ppm of4-carboxybenzaldehyde and about 40 ppm of ash as typical impurities.After air in the autoclave was purged with nitrogen, the pressure wasreduced and the mixture was gradually heated up to 60 C. Then, theautoclave was charged with ethylene oxide kept at a pressure of 4 Kg/cmwhile stirring. At the same time, 60 parts of the crude terephthalicacid was charged into the autoclave for 60 minutes at a substantiallyconstant rate. After completion of the addition of the crudeterephthalic acid, the reaction was further continued for 3 minuteswhile introducing ethylene oxide into the autoclave to decrease theamount of unreacted terephthalic acid. Then, the pressure in theautoclave was reduced to atmospheric pressure to recover unreactedethylene oxide. After a major part of water was distilled off byheating, 650 parts of nbutyl acetate was added to the reaction mixture,and the resulting diglycol ester and a small amount of ethylene glycolwere separated by extraction from the catalyst and unreactedterephthalic acid while removing the remaining water by azeotropicdistillation. The

extracted solution was added with about 6 percent by weight of powderyactive clay based on the diglycol ester contained in the solution,stirred for 10 minutes, filtered and then cooled to separate thediglycol ester. The active clay was substantially not effective fordecoloring, but was effective for removing metal impurities contained inthe raw materials and a very small amount of catalyst (alkali metalion).

The resulting crystals were slightly yellow. The crystals were decoloredby dissolving in about times amount by weight of hot water and treatingwith about 2.5 percent by weight of powdery active carbon. After theactive carbon was removed the hot solution was cooled to separatecolorless crystals. The crystals were added into 0.02 percent by weightof antimony oxide and polymerized for about 3.5 hours under a reducedpressure to obtain a polymer having an intrinsic viscosity of 0.68, amelting point of 268 C and an excellent whiteness.

A sample of the reaction mixture before the extraction with n-butylacetate was analyzed. 40 parts of the ethylene oxide was reacted, andthe conversion of ethylene oxide into ethylene glycol was 4 percent, andthat of ethylene oxide into diethylene glycol and diethylene glycolester was only 0.6 percent.

EXAMPLE 6 In 100 parts of water was dissolved 42 parts of sodiumbicarbonate to prepare 5 mol/l of an aqueous solution. The resultingsolution was introduced into an autoclave equipped with a stirrertogether with 120 parts of crude terephthalic acid. After air in theautoclave was purged with nitrogen, the autoclave was heated up to 100 Cunder atmospheric pressure and then up to 130 C while keeping theautoclave air-tight. Then, ethylene oxide was introduced into theautoclave under a pressure of 7 Kg/cm for 20 minutes while stirring. Thepressure in the autoclave was reduced to atmospheric pressure to recoverunreacted ethylene oxide. Heating was further continued to remove waterfrom the reaction mixture. Then, the reaction mixture was subjected toan extraction treatment with a mixed solvent composed of 300 parts ofn-butanol and 200 parts of xylene to separate catalyst and unreactedterephthalic acid as impurities. The extracted solution was cooled toseparate diglycol ester. The resulting diglycol ester was dissolvedagain in about 5 times amount of hot water based on the diglycol ester,and the solution was treated with about 5 percent by weight of granularactive carbon based on the diglycol ester and cooled to obtain crystalsof purified diglycol ester. A part of the crystals were recrystallizedfrom about two and one-half times amount of methanol to obtain highlypurified diglycol ester.

The two diglycol esters before and after the recrystallization withmethanol were polymerized in the presence of 0.01 percent by weight ofantimony acetate under the same condition of 0.5 mmHg, 280 C and 4 hoursto obtain substantially same colorless transparent polymers,respectively. The intrinsic viscosity of the polymer when the diglycolesters were recrystallized from methanol, was 0.66, and that of thepolymer when the diglycol ester was not recrystallized from methanol was0.64. The melting point of polymer, when the diglycol ester wasrecrystallized from methanol was 268 C, and that of polymer, when thediglycol ester was not recrystallized from methanol was 267 C.

A sample of the reaction mixture before the extraction with the mixedsolvent composed of n-butanol and xylene was analyzed. 40 percent of theethylene oxide was reacted, and the conversion of ethylene oxide intoethylene glycol was 19 percent, and that of ethylene oxide intodiethylene glycol and diethylene glycol ester was 4.4 percent.

EXAMPLE 7 Terephthalic acid and ethylene oxide were reacted under thesame condition as described in Example 5, except that medium gradecolorless crystalline terephthalic acid containing about 500 ppm of4-carboxybenzaldehyde and about 10 ppm of ash as typical impurities wasused. The reaction product was sub- 20 jected to an extraction treatmentwith the use of nbutyl acetate to separate unreacted raw materials andcatalyst, and the extracted solution was treated with active clay in thesame manner as described in Example 5. Then, the solvent wasconcentrated to obtain a melt of diglycol ester. The melt was added with0.04 percent by weight of antimony acetate, heated and polymerized forabout 3 hours under a reduced pressure to obtain a polymer having anintrinsic viscosity of 0.64, a melting point of 266 C and an excellentwhiteness.

EXAMPLE 8 In 100 parts of water was dissolved 12 parts of sodiumhydroxide, and the resulting solution was introduced into an autoclaveequipped with a stirrer together with 100 parts of highly pureterephthalic acid. After air in the autoclave was purged with nitrogenunder atmospheric pressure, the autoclave was heated'up to 100 C. Then,the autoclave was charged with ethylene oxide kept at a pressure of 4Kg/cm for minutes while stirring. After the pressure in the autoclavewas reduced to atmospheric pressure to recover unreacted ethylene oxide,heating was further continued to remove water. Then, 500 parts ofn-butyl acetate was added to the reaction mixture, and the resultingmixture was heated up to 120 C, and undissolved substances were filteredoff. The extracted solution was concentrated to obtain 97 parts ofcrystals of a mixture composed of diglycol ester and ethylene glycol andhaving a melting point of C. The resulting mixture had an acid value of1.8 (mg KOH/g) and contained 5 ppm of sodium. A part of the crystals washeated at 280 C for 3 hours under a pressure of 0.5 mmHg in the presenceof an antimony acetate catalyst to obtain a colorless transparentpolymer having an intrinsic viscosity of 0.64 and a melting point of 263C. The undissolved substances were 47 parts, contained terephthalicacid, sodium terephthalate, terephthalic acid monoglycol ester andsodium salt of terephthalicacid monoglycol ester, and were able to beused again in the next reaction.

COMPARATIVE EXAMPLE 4 The same reaction mixture as produced in Example 8was distilled to remove water therefrom and then 500 parts of n-butanolwas added thereto. The resulting mixture was heated to 110 C and thenundissolved substances were filtered off. The filtrate was concentratedto obtain 99 parts of a crystal having a melting point of 94 C and anacid value of 5.4. A part of the crystal was heated at 280 C under apressure of 0.5 mmHg in the presence of antimony acetate as a catalyst,but the polymer obtained became opaque and yellowish brown.

in general, when the extraction is carried out with a lower alcohol, thealkali metal in the catalyst is apt to be incorporated into theextracted solution, so that is is necessary to effect a treatment withactivated clay or ion exchange resin or a crystallization from solvent.This tendency is improved by mixing with a large amount of other solventhaving a lower polarity or by using a higher alcohol, but in many cases,it is usually necessary to effect the same treatment as described in thefollowing Example 9 which uses acetonitrile or dioxane.

EXAMPLE 9 The same reaction mixture as produced in Example 8 wasextracted with 500 parts of various solvents as mentioned below toobtain a result shown in the following Table 2.

Note: The sodium content was calculated as a single substance of Na.

The melts of the diglycol esters obtained by using methyl ethyl ketoneand dichloroethane were directly polymerized at 280 C under a pressureof 0.5 mmHg in the presence of antimony acetate as a catalyst to obtainsubstantially colorless and transparent polymers having intrinsicviscosities of 0.66 and 0.63 and melting points of 264 C and 263 C,respectively.

In case of acetonitrile and dioxane, the resulting melts were added witha substantially equimolar amount of phosphorous acid based on the sodiumcontent and then polymerized in the same manner as described above toobtain slightly grey polymers having intrinsic viscosities of 0.63 and0.68 and melting points of 263 and 265 C, respectively.

COMPARATIVE EXAMPLE The same reaction mixture as produced in Example 8was extracted with toluene at 100 C, and in this case 3,500 parts oftoluene was required. The obtained mixture of diglycol ester andethylene glycol had an acid value of 4.1 and a sodium content of 200ppm.

EXAMPLE 10 The same reaction mixture as produced in Example 8 wassubjected to an extraction treatment with 500 parts of an organic acidester as mentioned below. The obtained results are shown in thefollowing Table 3.

TABLE 3 Extraction Acid value Sodium Solvent temperature of extractcontent for extraction s /s) (pp Methyl acetate 50 2.] 9 Ethyl acetateL9 7 Methyl propionate 2.l 9 Ethyl formate 50 2.2 10

As seen from the above table, these organic acid esters show aremarkable separating effect similar to that in n-butyl acetate. Thethus obtained mixture of diglycol ester and ethylene glycol waspolymerized at 280 C under a pressure of 0.5 mmHg in the presence ofantimony acetate as a catalyst to obtain a colorless and transparentpolymer having an intrinsic viscosity of 0.62 to 0.68 and a meltingpoint of 263 to 264 C. Regarding the color tone (whiteness) of thepolymer, the organic acid esters are most excellent extracting agent.

EXAMPLE 1 1 37.2 parts of sodium carbonate was dissolved in parts ofwater to prepare 6 mol/l of an aqueous solution. This solution and partsof terephthalic acid were charged into an autoclave equipped with astirrer and heated to 100 C under atmospheric pressure after air in theautoclave was purged with nitrogen. Then, ethylene oxide was charged,while stirring, under a pressure of 4 Kg/cm for 40 minutes. The pressureof the reactor was returned to atmospheric pressure and unreactedethylene oxide was recovered. Then, the resulting reaction mixture wasadded with 500 parts of dioxane and heated to remove an azeotropicmixture of water and dioxane (boiling point: 87.8 C, water content:17.2percent), and thereafter undissolved substances were filtered off. Thefiltrate was concentrated to recover dioxane and 0.015 part of antimonyoxide was added, and then the resulting mixture was maintained at 280 Cunder a pressure of 0.5 mmHg for 3 hours to obtain a substantiallycolorless and slightly opaque polyethylene terephthalate having amelting point of 265 C and an intrinsic viscosity of 0.68.

EXAMPLE 12 24 parts of sodium hydroxide was dissolved in 100 parts ofwater to prepare 6 mol/] of an aqueous solution. This solution and 130parts of terephthalic acid of high purity were charged into an autoclaveand heated to 100 C under an atmospheric pressure after air was purgedwith nitrogen. Then, propylene oxide was charged, while stirring, undera pressure of 4 Kg/cm for 60 minutes. The pressure of the reactor wasreturned to atmospheric pressure and unreacted propylene oxide wasrecovered and further heating was continued to remove water. Then, thereaction mixture was added with 2,000 parts of xylene and heated to 130C and then undissolved substances were filtered off. The filtrate wasconcentrated to recover xylene and 0.05 part of antimony acetate wasadded thereto, and then the resulting mixture was maintained at 280 Cunder a pressure of 0.5 mmHg for 4 hours to obtain a colorless andtransparent polymer having a melting point of 106 C and an intrinsicviscosity of 0.26.

EXAMPLE 13 24 parts of sodium hydroxide was dissolved in 100 parts ofwater and the resulting solution together with 130 parts of isophthalicacid was charged into an autoclave and heated to 100 C under atmosphericpressure after air was purged with nitrogen. Then, ethylene oxide wascharged, while stirring, under a pressure of 4 Kg/cm for 35 minutes. Thepressure of the reactor was returned to atmospheric pressure andunreacted ethylene oxide was recovered and further heating was continuedto remove water. Thereafter, the reaction mixture was added with 500parts of dichloroethane and heated to 80C,'and then undissolvedsubstances were filtered off. The filtrate was concentrated to recoverdichloroethane and 0.015 part of antimony oxide was added, and then theresulting mixture was maintained at 280 C under a pressure of0.5 mml-lgfor 3 hours to obtain a colorless and transparent polyethyleneisophthalate having a melting point of 150 C and an intrinsic viscosityof 0.57.

EXAMPLE 14 An aqueous solution of 12 parts of sodium hydroxide and 7.2parts of lithium hydroxide dissolved in 100 parts of water was chargedtogether with 130 parts of terephthalic acid of high purity into anautoclave and heated to 100 C under atmospheric pressure after air waspurged with nitrogen. Then, ethylene oxide was charged, while stirring,under a pressure of 4 Kglcm for 30 minutes. The pressure of the reactorwas returned to atmospheric pressure and unreacted ethylene oxide wasrecovered and further heating was continued to remove water. Then, thereaction mixture was added with 100 parts of n-butanol and 900 parts ofxylene and heated to 1 C, and then undissolved substances were filteredoff. The filtrate was concentrated to recover n-butanol and xylene and0.04 part of antimony acetate was added, and then the resulting mixturewas maintained at 280 C under a pressure of 0.5 mmHg for 3 hours toobtain a substantially colorless and transparent polyethyleneterephthalate having a melting point of 266 C and an intrinsic viscosityof 0.68.

EXAMPLE 7.2 parts of lithium hydroxide was dissolved in 100 parts ofwater to prepare 3 mol/l of an aqueous solution, which was chargedtogether with 150 parts of terephthalic acid of high purity in anautoclave equipped with a stirrer and heated to 90 C under at-'mospheric pressure after air was purged with nitrogen. Then, ethyleneoxide was charged, while stirring, under a pressure of 3 Kg/cm for 90minutes. The pressure of the reactor was returned to atmosphericpressure and unreacted ethylene oxide was recovered and further heatingwas continued to remove water. The reaction mixture was added with 800parts of n-butyl acetate and heated to 120 C, and then undissolvedsubstances were filtered off. Thereafter, the filtrate was concentratedto recover n-butyl acetate and 50 parts of terephthalic acid of highpurity and 0.06 part of antimony acetate were added thereto, and thenthe temperature was gradually raised. As the inner pressure increasedduring the temperature rising, water was removed while maintaining thepressure to 3 Kg/cm After the temperature reached 280 C, the reactionmixture was polymerized under a pressure of 0.5 mmHg for 4 hours toobtain a colorless and transparent polyethylene terephthalate having anintrinsic viscosity of0.66 and a melting point of 265 C.

EXAMPLE 16 To parts of the undissolved substances separated in Example 1were again added parts of water and 100 parts of terephthalic acid ofhigh purity and the resulting mixture was charged into an autoclave andheated to 100 C under atmospheric pressure after air was purged withnitrogen and then ethylene oxide was charged thereinto under a pressureof 4 Kg/cm for 40 minutes. The pressure of the reactor was returned toatmospheric pressure and unreacted ethylene oxide was recovered andfurther heating was continued to remove water. Then, the reactionmixture was added with 500 parts of acetonitrile and undissolvedsubstances were filtered off at 70 C. The filtrate was added with 0.05part of antimony acetate and heated to recover acetonitrile and thenmaintained at 280 C under a pressure of 0.5 mml-lg for 3.5 hours toobtain a substantially colorless and transparent (slightly light yellow)polyethylene terephthalate having an intrinsic viscosity of0.68 and amelting point of 265 C.

What is claimed is:

l. A method for producing polyester which comprises:

reacting benzenedicarboxylic acid with alkylene oxide having from two tosix carbon atoms, in water containing from 2.7 to 10 moles of alkalimetal ion per one liter of water, the reaction being carried out at atemperature in the range of 60 to C. and there being present in thereaction system undissolved alkali metal salt of saidbenzenedicarboxylic acid, to produce a reaction product containingdiglycol ester;

contacting the reaction product with an organic sol vent selected fromthe group consisting of esters, ethers, ketones, benzene and alkylbenzenes, halogenated hydrocarbons, nitriles, alcohols and mixturesthereof, to obtain an essentially waterfree, organic solvent solutioncontaining dissolved diglycol ester;

concentrating and/or crystallizing the solution to remove said solventand then effecting a polycondensation reaction.

2. The method as claimed in claim 1, wherein said alkali metal ion issodium or lithium.

3. The method as claimed in claim 1, wherein said alkali metal ion islithium.

4. The method as claimed in claim 1, wherein the amount of said alkalimetal ion in the reaction system is 3 to 8 moles per liter of water.

5. The method as claimed in claim 1, wherein said organic solvent isselected from the group consisting of chlorinated hydrocarbons, organicacid esters'and ketones.

6. The method as claimed in claim 1, wherein said benzenedicarboxylicacid is selected from the group consisting of terephthalic acid,isophthalic acid and mixtures thereof.

7. The method as claimed in claim 1, wherein the amount of saidbenzenedicarboxylic acid in the reacamylene oxide and hexene oxide.

9. The method as claimed in claim 1, wherein said organic solvent isused in an amount of 1 to 50 times the weight of the reaction mixture.

1. A method for producing polyester which comprises: reacting benzenedicarboxylic acid with alkylene oxide having from two to six carbon atoms, in water containing from 2.7 to 10 moles of alkali metal ion per one liter of water, the reaction being carried out at a temperature in the range of 60* to 140* C. and there being present in the reaction system undissolved alkali metal salt of said benzenedicarboxylic acid, to produce a reaction product containing diglycol ester; contacting the reaction product with an organic solvent selected from the group consisting of esters, ethers, ketones, benzene and alkyl benzenes, halogenated hydrocarbons, nitriles, alcohols and mixtures thereof, to obtain an essentially water-free, organic solvent solution containing dissolved diglycol ester; concentrating and/or crystallizing the solution to remove said solvent and then effecting a polycondensation reaction.
 2. The method as claimed in claim 1, wherein said alkali metal ion is sodium or lithium.
 3. The method as claimed in claim 1, wherein said alkali metal ion is lithium.
 4. The method as claimed in claim 1, wherein the amount of said alkali metal ion in the reaction system is 3 to 8 moles per liter of water.
 5. The method as claimed in claim 1, wherein said organic solvent is selected from the group consisting of chlorinated hydrocarbons, organic acid esters and ketones.
 6. The method as claimed in claim 1, wherein said benzenedicarboxylic Acid is selected from the group consisting of terephthalic acid, isophthalic acid and mixtures thereof.
 7. The method as claimed in claim 1, wherein the amount of said benzenedicarboxylic acid in the reaction system is more than equivalent of the alkali metal ion in the reaction system.
 8. The method as claimed in claim 1, wherein said alkylene oxide is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, amylene oxide and hexene oxide. 